WASHINGTON – The federal effort to provide drones regular access to U.S. skies faces significant hurdles and will not meet a September 2015 deadline set by Congress, a government watchdog said Monday.

Despite years of research, the Federal Aviation Administration hasn’t figured out what kind of technology unmanned aircraft should use to avoid crashing into other planes and to prevent lost links with ground control stations, Matthew Hampton, the Transportation Department’s assistant inspector general for aviation, said in a report.

The FAA also hasn’t set standards for certifying the safety of drone designs and manufacture like those that exist for manned aircraft, the report said. Nor has the agency developed standard procedures for air traffic controllers to guide drones. There is no adequate program for training controllers how manage unmanned aircraft. And criteria for training “pilots” who remotely control drones from the ground have yet to be developed.

Until the FAA resolves these problems and others, the effort to integrate drones into the national airspace “will continue to move at a slow pace, and safety risks will remain,” the report said.

FAA officials, defending the agency’s record, said in a statement that despite the inspector general’s findings the FAA “has made significant progress” toward giving drones wider access to U.S. skies “even as it dealt with disruptions” due to automatic, government-wide spending cuts and a three-week partial government shutdown.